The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery.
A non-aqueous electrolyte secondary battery that is currently commercially available uses LiCoO2 as a positive electrode active material and a carbon material as a negative electrode active material. Charge-discharge capacity of a non-aqueous electrolyte secondary battery usually depends on the active materials used for the positive and negative electrodes. Therefore, an active material that can provide greater capacity to a battery has been sought.
Recently, an amorphous material has been proposed as a material to provide greater capacity than LiCoO2 (Japanese Patent Laid-open Publication No. 11-283627). Among various materials, a manganese oxide is the most promising especially for use as a positive electrode active material because of raw material cost and the amount of resources (Japanese Patent Laid-open Publication Nos. 9-171817 and 11-297323, and J. J. Xu et al., Electrochemical and Solid-State Letters, 1, 1-3 (1998) et al.).
However, the amorphous manganese oxide proposed in Japanese Patent Laid-open Publication No. 11-297323 includes K (potassium). When the manganese oxide is used as a positive electrode material for a lithium secondary battery, K ions move between a positive electrode and a negative electrode together with Li ions, and adversely affect discharge potential and the like.
The amorphous manganese oxide proposed in Electrochemical and Solid-State Letters, 1, 1-3 (1998) and Japanese Patent Laid-open Publication No. 9-171817 has a great discharge capacity when it is used as an active material for a lithium secondary battery, but improvement of load characteristics is required. That is, a battery having the amorphous manganese oxide does not have a great discharge capacity with regular current because the load characteristics of the amorphous manganese oxide are not as good as LiCOO2.
Objects of the present invention are to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and to provide a non-aqueous electrolyte secondary battery having the positive electrode active material.
The present invention provides a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a complex oxide wherein said complex oxide is substantially amorphous and comprises Mn and M,
where M is an element selected from the group consisting of Ni, Co, Fe, Cu, Al, Mg, Si, Sc, Ti, Zn, Ga, Ge, Nb, Rh, Pd and Sn; and
a molar weighted sum of oxidation states of elements except for oxygen is more than 3.8 and not greater than 4.2 (3.8xe2x89xa6molar weighted sum of oxidation statesxe2x89xa64.2).